The present invention relates to an apparatus for lifting a sow from a mold and more specifically to such an apparatus which employs a vacuum in removing the sow. A sow is an extremely heavy block of metal that is cast into a mold and which is typically at a relatively high temperature when it is removed from a mold.
In a metal purification and casting operation, molten metal is typically poured into a mold and then allowed to solidify. The mold is often coated with a mold release material to facilitate removal of the cast sow or block of metal following casting. Because the molds are typically reused and need to be made available more quickly for a subsequent pouring and sow removal cycle, the temperature of the sows can be near the melting point of the metal at the time of sow removal. To assist in the solidification of at least an outer shell of the sow, molds and the molten metal are commonly sprayed with water or are otherwise cooled to accelerate the solidification of the metal.
In a known approach, a plurality of molds are interconnected in a sow train or wheel with the molds traveling on a track. The molds travel between a sow pouring location, at which the mold is filled with molten metal, a sow removal location, at which the solidified sow is removed from the mold, and back to the sow pouring location. It is not unusual for the plurality of molds to be interconnected in the form of an endless loop of cars which travel along a track between these locations or on a rotating wheel.
In one conventional approach for removing sows from a mold, each mold is inverted as it reaches a sow removal location to dump the sow from the mold. The sow is then returned to its upright position for movement, such as by a forklift, to a sow stacking or collecting location. In the case of sows of aluminum, it is not unusual for a cast sow to weigh between 1200 pounds and 1500 pounds. In addition, it is not unusual for an aluminum sow to be at a temperature of 500.degree. F. to 700.degree. F., or higher, at the time the sow is removed from the mold. Consequently, to the extent sows need to be turned over for subsequent handling, the risk of a worker being. inadvertently burned by coming into contact with the sow is increased. Also, the step of inverting or tilting a mold to eject a sow requires mold tilting equipment and can add to the time required to remove a sow and return a mold into position for a subsequent metal pour cycle.
In another approach for removing sows from a sow train, keys are positioned in a mold before molten metal is poured. These keys are typically positioned adjacent to a wall of the mold and are partially embedded in the sow during casting. Following solidification of a sow, the keys are removed to leave tong receiving pockets in the sow. The combination of pockets formed by these keys provide a gripping location for tongs which are used to remove the sow from the mold. The tongs are typically coupled to a hoist or overhead crane which lifts the tongs and sow from the mold. Typically, sledge hammers are used to beat the keys free from the sow prior to using the tongs. It is extremely noisy to use sledge hammers to knock the keys free. In addition, workers using sledge hammers are in close proximity to the hot sows and thus are at risk of being burned even though relatively expensive safety garments and gloves are worn to help reduce this risk.
One aluminum manufacturing company is understood to have used a vacuum for lifting a sow from a mold. Initially, a low temperature seal was understood used in an attempt to establish a seal between the lifting device and the sow. To cool the sow to the point where the low temperature gasket would not be damaged by the high temperatures involved, the temperature of the sow was reduced prior to sow removal. As a result, cooling water used in solidifying the sow would tend to remain in the mold and not totally evaporate as the mold in a sow train reached the pouring location. Molten aluminum poured into water causes the rapid expansion of steam and spattering of aluminum, risking injury and damage. It is also understood that this aluminum manufacturing company is now utilizing a different gasket material, namely multiple layers of a silicon and fiberglass material stacked to form a gasket of a square or rectangular cross section in combination with a vacuum device to lift a sow from a mold. This gasket material allows the sow to be removed at higher temperatures. However, to form a seal with the upper surface of a sow when such a gasket is used, it is understood that this company requires equipment or operates a sow train to solidify a sow in a manner that reduces surface variations normally present in the upper surface of a solidified sow. Although the exposed upper surface of a partially solidified sow in a mold appears to be quite uniform and planar, in the absence of such equipment or process step, typically the upper sow surface has variations of from one-quarter to three-quarters of an inch or more from a horizontal plane.
In these prior art approaches, if a lifted sow should slip, workers are exposed to a risk of injury, due to the weight of the sow and/or the high temperature of the sow.
Thus, a need exists for an improved sow lifter which is directed toward overcoming the above and other limitations and disadvantages of the prior art.